Echo suppressor



March 26, 1929. s. B. WRIGHT ECHO SUPPRESSOR Filed April 23 1926 IN VEN TOR 61B. W

z A TTORNEV Patented Mar. 26, 1929.

UNITED STATES PATIENT @FFICE'.

SUMNER B. WRIGHT, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAI'I-I COMPANY, A CORPORATION OF NEW YORK.

ECHO SUPPRESSOIR.

Application filed April 23,

This invention relates to voice operated devices for suppressing echoes and singing in two-way transmission systems, and more particularly to arrangements whereby the voiceoperated devices may be located in the twowire part of such a system.

Two-way transmission systems are usually so arranged that certain portions of the circuit are operated on a two-wire basis, while other parts of the circuit, more particularly where repeaters are located, are operated on a four-wire basis. In the four-wire parts of the system, there will be a tendency to sing if the total amplification of the four-wire loop 1 exceeds the total loss. F urt-hermore when transmission takes place in one direction over such a system, echo currents may be transmitted back from the terminals or from other reflection points in the system.

It has therefore been proposed to associate echo suppressors with the four-wire parts of the systems, these echo suppressors functioning to prevent transmission in one direction while transmission is taking place in the other directions. In accordance with the present invention, however, it is proposed to so arrange the echo suppressors that they may be connected to and operated from the two-wire part of the system. More specifically, it is proposed by the present invention to provide two echo suppressors in the two-wire part of the system, with a delay circuit interposed between the echo suppressors having such a circuit control that the suppressor which is operated first will be effective, and the suppressor which is operated later will be unable to perform its usual function. In this manner, the echo suppressors may exercise different controls over the circuit, depending upon the direction of transmission.

The invention will now be more fully understood from the following description whenread in connection with the accompanying drawin Figure 1 of which is a circuit dia- 4 gram il ustrating the preferred embodiment of the invention, and Fig. 2 is a diagram showing a typical delay circuit.

Referring to Fig. 1, the invention is shown applied to a radio system of communication, but it will be understood that it is equally applicable to other types of systems. The circuit as illustrated comprises a schematical- 1y shown radio transmitter T, and a schematically shown radio receiver R, each of which may be of any well-known type or construc- 1926. serial No. 104,173.

telephone subscribers set in any well-known manner, as, for example, through a 22-type repeater comprising amplifiers AE and AW, balancing networks N and N, etc., all arranged in a manner well understood in the art.

A delay network X may be interposed in the two-wire line L. This delay network may be of any known type. For example, it may assume the form of a low-pass filter such as is illustrated in Fig. 2. At one side of the delay circuit X, an echo suppressor unit comprising a voice current detector or rectifier DE and its controlled relay ER is bridged across .the line L. The detector or rectifier is indicated conventionally and may be of any t pe well-known in the art, preferably inclu ing suitable amplifying means for amplifying the voice currents which are to be its associated relay WR is bridged across the" line L on the opposite side of the delay circuit X. The relays ER and WR exercise a joint control over a switching relay 21 which in turn controls the circuits of relays 22 and 23. The trunk TE is normallyshort circuited over the back contact of relay 22, thereby preventing singing from the transmitting an; tenna to the receiving antenna and thence through the trunks TW and TE in tandem. Relay 23, when energized, is adapted to short circuit the trunk TW to prevent transmission from east to west.

The relays used are such that while relays 22 and 23 operate promptly in response to the effect of voice currents, they do not return to their normal condition until a period has elapsed after the cessation of the voice ourrents which is long enough to insure that all echoes have died out.

It will, of course, be understood that the transmission loss introduced by the delay network X may be made up by the 22 repeater v interposed between line sections L and L.

The operation is as follows: Normally, the trunk TE is short circuited so that transmission can not take place from west to east. The trunk TW is normally operative, however, and signals radiated from the distant,

transmitting station will be received. If a subscriber talks over the line L, the transmission passes through the 22 repeater to the line section L and thence through the delay network X. In the meantime, part of the energy passes into the voice current detector DE and is rectified to operate the relay ER. This relay closes the circuit through the lefthand winding of the relay 21. Relay 21 pulls up its armature, thereby opening the circuit of its right-hand winding which is controlled by the relay WR, and at the same time it closes the circuit of relays 22 and 23. Relay 22 removes the short circuit from the trunk TE of the four-wire part of the system, while at the same time the relay 23 short- 20. circuits the trunk TW of the four-wire part of the system. As a result, the system is now in a condition to transmit from west to east. Furthermore, any energy radiated by the transmitter T and received locally by the receiver R will be ineffective due to the short circuit acrossthe trunk TW. When the voice signals have passed through the delay network X, a part of the energy is transmitted into the trunk TE and through the repeater RE to be radiated b theradio transmitter T. Another part 0 the energy enters the voice current detector DW and is rectified to operate the relay WR. The operation of this relay produces no effect, however, as the relay 21 has already been energized, so that "the right-hand circuit of the relay 21 is opened. The delay circuit X therefore performs a dual function; in that it delays the operation of the relay'WR until after the re lay ER has seized control of the circuit. It

v to talk, the echo suppressor'rela ER is deenergized, and, a moment later, t e echo suppressor WR is also deenergized. Relay 21, which may be somewhat slow to release, will release its armature after an interval, thereby opening the circuits of relays 22 and 23. This again restores the short circuit to the trunk TE and removes the short circuit from the trunk TW, a suificient interval having elapsed to insure that all echoes have died out. The circuit is now in condition to transmit from east to west.

If a subscriber associated with the distant intercommunicating set talks, the energy so radiated will be received by the radioreceiver R, and the voice signal detected therefrom in the usual manner. The detected voice cur- .rents pass through the repeater RW and over the trunk TW to the line section L. The energy is prevented from passing over the trunk TE to the radio transmitter T by the short circuit controlled by the relay 22. As the voice energy enters the delay circuit X,

a portion of said energy is diverted into the not to cause it to pull up its armature. After the voice energy passes through the delay circuit X, a part of it is diverted to operate the relay ER of the other echo suppressor unit. This closes the circuit through the left-hand winding of the relay 21. The relay 21 is differentially wound so that its windings ope pose each other,.with the result that the current flowing through the left-hand windin is ineffective to actuate the relay. Accor ingly, relays 22 and '23 remain deener ized during the time the transmission is ta ing place from east to west. When the subscriber at the distant station ceases talking, relay WR and relay ER release, and the circuit is restored to normal. Relay WR should, of. course, hang on until relay ER releases as otherwise relay 21 might operate.

It will be clear that the operation of the circuit above described depends upon which of the two echo suppressor units is operatedfirst, and this in turn is determined by the direction from which the-voice currents arrive. It will also be clear that as the circuit is only operative in one direction at a time, it is unnecessary to rovide balancin arrangements between t e two-wire and ourwire parts. of the system.

It will also be-obvious that the general principles herein disclosed may be embodied in many other organizations widely diflerent from those illustrated without de arting from the spirit of the invention, as de ed in the following claims.

What is claimed is:

1. In a transmission system comprising a two-wire section and a four wire section, echo suppressor units so associated with the twowire section as to be both operable by transmission in one direction thereover, means in said section to delay transmission from one of said units to the other, means operative to determine which branch of the four-wire section of the system shallbe operated, "and means whereby the determination exercised by said last mentioned means will be dependent upon which echo suppressor unit is first operated.

2. In a signaling system having a two-wire section and a four-wire section, a pair of echo suppressor units associated with said twowire secti0n,-means in said section to delay transmission from one unit to the other, means res onsive 'when one of said units is actuated efore the other to render one branch of the four-wire section operative and the other branch inoperative, and means operating when the other unit is operated first to render said first branch of the fourwire section inoperative and said last branch operative.

3. Iii a signaling system comprising a twowire section and a four-wire section, a relay normally operative to disable one branch of the four-wire section while permitting the second branch of said section to remain 0 rative, a pair of echo suppressor units associated with said two-wire branch, a delay circuit interposed between said units, and means whereby when one of said units isoperated before the other, said relay will be actuated to render said first mentioned branch operative and to disable said second branch, and whereby when the other unit is operated first,

said relay will cause said first branch of the four-wire section to be disabled and said second branch to be operated.

4. In a signaling system having a radio transmitter and a radio receiver, separate branches extending from said transmitter and receiveryrespectively, to'a two-wire line, a

pair of echo suppressor units connected to said two-wire line, a dela circuit interposed between the said units, re a means normally functioning to disable the ranch leading to said transmitter, means operative when one of said units is actuated before the other to cause said rela means to render the branch leading to said transmitter operative while disabling the branch leading to the receiver, andwhereby when the other of said units is actuated first, said rela means will disable the branch leading to the transmitter, and render the branch leading to the receiver operative.

In testimony whereof, I have si edmy name to this specification this 22n day of April, 1926. a

SUMNER B. WRIGHT. 

